<template>
  <div class="pagination">
    <button @click="$emit('currentPage',pageNo - 1)" :disabled="pageNo == 1">上一页</button>
    <button v-if="startAndEnd.start > 1" @click="$emit('currentPage',1)">1</button>
    <button v-if="startAndEnd.start > 2">···</button>

    <button
      v-for="page in startAndEnd.end"
      :key="page"
      v-if="page >= startAndEnd.start"
      @click="$emit('currentPage',page)"
      :class="{active :pageNo == page}"
    >
      {{ page }}
    </button>

    <button v-if="startAndEnd.end < totalPage - 1">···</button>
    <button v-if="startAndEnd.end < totalPage"  @click="$emit('currentPage',totalPage)">{{ totalPage }}</button>
    <button @click="$emit('currentPage',pageNo + 1)" :disabled="pageNo == totalPage">下一页</button>

    <button style="margin-left: 30px">共 60 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["total", "pageSize", "pageNo", "pagerCount"],
  computed: {
    // 分页器一共多少页 【总页数 / 每页有多少条】
    totalPage() {
      // 超出向上取整
      return Math.ceil(this.total / this.pageSize);
    },
    // 计算出连续的五个字 开头 与结尾
    startAndEnd() {
      // 计算出连续的页码  开始与结束这两个数字
      let start = 0,
        end = 0;
      const { totalPage, pageNo, pagerCount } = this;

      // 特殊情况：总共页数小于连续页码数
      if (totalPage < pagerCount) {
        start = 1;
        end = totalPage;
      } else {
        // 正常情况：总页数大于连续连续页码数
        start = pageNo - parseInt(pagerCount / 2);
        end = pageNo + parseInt(pagerCount / 2);

        // 约束开始与结束在合理的范围内
        // 约束开始
        if (start < 1) {
          start = 1;
          end = pagerCount;
        }

        // 约束结束
        if (end > totalPage) {
          end = totalPage;
          start = totalPage - pagerCount + 1;
        }
      }

      // 返回开始的值 和结束的值
      return { start, end };
    },
  },
};
</script>

<style lang="less" scoped>
.pagination {
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>